This invention relates to a lock for a differential which is self-setting.
Differentials are utilized to provide rotational drive to two separate shafts. The differential allows the two shafts to rotate at different speeds relative to each other. Typically, a differential case surrounds the two shafts, and a single drive input comes into the differential. At least one, and typically two, outputs are driven by the differential. The differential allows relative rotation between the outputs.
Under certain conditions, it is desirable to prevent or limit any relative rotation between the two shafts. As an example, the two shafts often drive the two wheels on an axle of a vehicle. Relative rotation can occur during turning, and is desirable. However, relative rotation can also occur such as when one of the wheels is slipping on ice. In such circumstances, it may be undesirable to have relative rotation. Thus, differentials are often provided with a lock feature. Typically this lock feature is manually actuated to prevent relative rotation. In this way, a slipping wheel will be forced to rotate at the same speed as the other wheel. The manually actuated locks have some drawbacks. They are driver skill and attention dependent. Thus, at times, a driver may not always have engaged the lock at a proper time. This may have caused unnecessary wear or damage to components. The same could happen if the driver does not disengage the lock at an appropriate time.
Differential locks have also been proposed which rely on exotic fluids which increase viscosity under certain circumstances.
There are also ms which are known as limited slip differentials. These are typically internal to the differential gears, and also have limitations. These systems typically use friction plates to create resistance to a relative speed of the axle shafts. A disadvantage of these systems is that they are constantly active regardless of relative speed or road condition. They are also dependent on the initial preload of the internal system, and some are operating torque dependent to produce torque in poor road conditions. Thus, these systems can only deliver low torque output when most needed (under extreme road conditions) to avoid detrimental effects to the normal vehicle performance. That is, the system must be set up such that it only becomes effective under extreme conditions, otherwise normal operation will be affected. Further, these systems have high wear of the friction materials and relatively high noise.
In general, the known differentials have required manual actuation and have been relatively complex and expensive. The fluid-based differential lock requires an exotic fluid, and is also not as effective as would be desirable.
In a disclosed embodiment of this invention, a differential lock member is moved at a speed dependent on the relative rotation between two components of a differential. As the lock member increases its speed, a fluid resists movement of the lock member. Thus, there is more resistance to movement of the lock member. As the lock member begins to move at a slower rate, it will cause the two differential components to rotate at a more equal speed. That is, as the lock member has its movement slowed, it will tend to cause the two differential components to rotate at a more equal speed.
In embodiments of this invention, the lock member is positioned between an inner shaft and the differential case at an outer peripheral surface. The lock member is driven axially along a shaft axis as the relative rotation between the shaft and the case increases. In preferred embodiments the lock member has a fluid path through its length. As the lock member is moved axially, it is forced against fluid chambers on each end. Fluid passes between the two chambers through the passage as the moving lock member moves within the chambers. A valve is preferably mounted on the passage. As the moving lock member increases its speed, the valve tends to close the passage. Thus, as the moving lock member increases its speed due to increasing relative rotation between the shaft and the case, the valve will limit flow of fluid. As the flow of fluid through the passage is limited, the ability of the lock member to move is also limited. As the lock member slows, it will tend to drive the shaft and case at a more equal speed together. In a most preferred embodiment, the valve is spring biased outwardly of the passage and forced into the passage by the fluid pressure. As the speed of the lock member increases, so will the fluid pressure acting on the valve.
In a preferred embodiment of this invention, the moving lock member is driven to move axially by relative rotation between the shaft and differential case by having a pin at one surface engaged in a axial groove in one of the case and shaft, and a pin in the other of the case and groove engaged in a cam. When there is relative rotation, the pin moves in the cam, which causes the lock member to move axially. Preferably, the cam is formed in the outer periphery of the shaft. Thus, as the shaft rotates relative to the case, the lock member moves axially and is constrained to rotate with the case.
In other features of this invention, the movable lock member is generally tubular in shape, and surrounds the shaft. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.